Miniature resistor networks (also known as circuit modules) are utilized in many electronics applications such as computers and other business equipment. The circuit modules may consist of a ceramic substrate having a plurality of resistors and conductive paths on one or both surfaces and connected to terminals secured to the substrate. The terminals may consist of a variety of metallic conductors attached by various methods to the substrate.
Cermet resistor networks are illustrated in the advertising brochures of resistor network manufacturers, such as the CTS Corporation Cermet Resistor Network Catalog 3755B. CTS Catalog 3755B illustrates a variety of resistor network configurations generally comprising alumina substrates having a plurality of terminals inserted in associated apertures disposed in an end of the alumina substrate. The terminals may be either round wires having an end force fitted into a noncomplementary shaped cavity in the substrate, or flat wires having an end force fitted into associated noncomplementary shaped openings and subsequently trimmed to shape. After insertion, the terminals are wave soldered to insure their electrical connection with conductive material disposed about and in the apertures into which the terminals are secured, and to provide corrosion protection for the portions of the terminals extending exteriorly of the alumina substrate. A resistor network having terminals attached and secured thereto by this method and the terminals coated by wave soldering, may be mounted onto a PC board having a plurality of holes for receiving the respective terminals, the terminals then connected to the PC board by wave soldering. The manner in which the terminals are anchored in the cavities in the end of the substrate, is described in commonly-owned U.S. Pat. Nos. 3,280,378 entitled "Means for Anchoring and Connecting Lead Wires and an Electrical Component," issued Oct. 18, 1966, and U.S. Pat. No. 3,346,774 entitled "Electrical Component Substrate with Cavities for Anchoring Lead Wires Therein," issued Oct. 10, 1967.
The prior art method for mechanically securing and anchoring terminals in the alumina substrate is schematically illustrated in FIGS. 1A and 1B. It comprises a method wherein a plurality of wires 1 are fed by gripping device 8 from reels 9 through a complementary group of open ended barrels 2 and into transmittal slots 5 (see FIG. 1A), the number of wires, barrels, and slots matching the number of associated cavities 6 in the end of the alumina substrate 7. A cut-off or blade device 3 moves downwardly to cut the wires to proper length, and while the cut-off device is extended and covers the back of the slots 5 (see FIG. 1B), compressed air is fed through a manifold 4 in the cut-off device and into the rear of each transmittal slot 5 so that the terminals are blown by compressed air through the slots and into the associated cavities 6 of the substrate 7 positioned adjacent the end of the slots 5. The blade device 3 and subjacent barrels 2 retract upwardly, the wires are advanced by gripping device 8, and the other steps repeated.
This prior art method has proved successful for the manufacture of resistor networks wherein the cut end of each terminal deforms and bites into the substrate cavity to securely anchor the terminal. A problem posed by this method is that both ends of the terminal have been cut by the blade device, i.e. after the cut and blow-in insertion, the blade device rises, the wires are advanced an appropriate length, the blade decends to cut the terminals to length, and then the terminals are blown into a substrate. Because the ends of the terminals exterior to the substrate have been cut, the exterior ends (although suitable for insertion into corresponding openings in a PC board) can cut or gouge metallic sockets into which the terminals might be inserted. Likewise, if the terminals are of a flat configuration as illustrated in Catalog 3755B, the cut exterior end of each terminal produces a nonuniform shaped, deformed end which can damage a socket into which the terminal is inserted, and therefore the cut exterior portions of the terminals are not suitable for use with a pluggable component such as a socket assembly. Additionally, solder coating the terminals will not satisfactorily protect the terminal from corrosion to provide a long wear life covering decades of years.
The problems facing the industry are how to provide a resistor network having a plurality of terminals anchored in the substrate whereby by the exterior ends of the terminals are uniformly shaped, such that there are no deformation marks, swaging, or irregularities which can cut into and damage a metallic socket when the terminals of the resistor network are inserted, and also how to increase the integrity and reliability of a protectively plated terminal so that the resistor network has a wear life and superior electrical conductivity for decades. Thus, there is needed for securement in a substrate both a plated terminal that will provide long term resistance to corrosion and superior electrical conductivity, plus a terminal whose exterior has not been deformed, cut, scratched, or swaged before, during, or after the process of inserting and anchoring the terminal in the substrate, and thereby may be utilized with a pluggable component so that the circuit module can be readily removed from the PC board as desired.